This invention relates to molded products obtained by curing a molding composition containing thermosetting (meth)acrylate liquid resins.
Unsaturated polyester resins are representative examples of thermosetting liquid resins. There are many molding methods for obtaining molded objects by curing compositions which contain such unsaturated polyester resins, including the compression method, the injection method, the hand lay-up method, the pultrusion method and also the resin transfer molding (RTM) and reaction injection molding (RIM) methods which are considered most ideal and economical.
Unsaturated polyester resins with low viscosity, however, are hard to obtain. If a composition is prepared by adding an inorganic filler to such a resin, its viscosity tends to increase significantly. If a molding composition has a high viscosity, it takes a long time to transfer it into a mold. If one attempts to prevent such an unreasonable increase in viscosity, this necessarily limits the amount of organic fillers that can be added. Another problem with unsaturated polyester resins is that, since they are made from phthalic acids or bisphenols and styrene is used as reaction dilutant (solvent), the content of aromatic hydrocarbons is high and hence that black smoke tends to be copiously generated when a molded object made from such unsaturated polyester resins is burnt. Methods for providing flame resistance to unsaturated polyester resin include the method of additionally using a water-containing inorganic filler such as aluminum hydroxide (Al.sub.2 O.sub.3.3H.sub.2 O), the method of using so-called flame-resistant unsaturated polyesters combining halogens, the method of adding a halogen-containing antiflame agent to a mixture of unsaturated polyester resin and a water-containing inorganic filler, and also the method of adding antimony trioxide in order to enhance the flame-resistant effect of a halogen. As long as unsaturated polyester resins are used, however, generation of a large amount of black smoke is inevitable by any of these methods when a molded object is burnt. It has been well known that the generation of such black smoke in large quantity makes it difficult for people to escape from the site of a fire and hence serves as the most serious cause of deaths at the time of a fire.
In order to solve this problem with prior art unsaturated polyester resins, U.S. Pat. No. 4,480,079 and EP197682 disclosed liquid resins composed of unsaturated urethane obtained from polymethylene polyphenyl polyisocyanate and hydroxy alkyl (meth)acrylate and alkyl (meth)acrylate. Because of the use of unsaturated urethane obtained from polymethylene polyphenyl polyisocyanate and hydroxy alkyl (meth)acrylate, however, such liquid resins have the following problems. Firstly, black smoke is still generated copiously when a molded object therefrom is burnt. If a composition containing a large amount of water-containing inorganic filler is used in order to prevent it, its viscosity becomes high and it affects the molding process adversely. Secondly, although use is made of compositions containing thermoplastic high molecular compound as a low profile agent, the effects of such thermoplastic high molecular compounds are weak at the time of molding.